Novel Design of an Integrated Pulp Mill Biorefinery for the ...

More documents

Recommendations

Info

The multi-tubular fixed bed reactor is a Low Temperature Fischer-Tropsch (LTFT) reactor ranging from 220-250 ºC. LTFT reactors are better suited for the creation of heavy hydrocarbons in the form of liquid wax. Later in the process, these long chain hydrocarbons are cracked to formed FTD [4, 71, 72, 74]. The multi-tubular fixed bed reactor can use either iron or cobalt catalysts. Catalyst poisoning can occur when coal or biomass is used in the creation of syngas. An advantage of the TFBR is that only the upper portion of the catalyst may be poisoned, allowing the remaining catalyst to be operational. However, to replace the catalyst in the TFBR, the reactor must be taken off line, which causes expensive downtime [72]. The slurry-phase bubbling-bed reactor (SPR) is a three phase reactor with solid, gas and liquid phases. It is also a LTFT reactor that can utilize both iron and cobalt catalyst. In the SPR small partials of catalyst are suspend in liquid while syngas bubbles propagate through the slurry. The reactor temperature is precisely controlled by steam-filled coils that snake through the slurry. The product hydrocarbons are drawn from the top of the slurry. Light hydrocarbons and un-reacted syngas exit through the top of the reactor. The SPR reactors have only recently become a viable reactor. The SPR was tested in the 1950’s and 1960’s; however a viable method of separating the catalyst from the wax product was not invented until 1990 by Sasol [72]. The SPR is also a LTFT reactor which can utilize both iron and cobalt catalysts. If a catalyst poison enters the SPR, all of the catalyst will be deactivated. Nonetheless, the key advantage of the SPR is that its catalyst can be replaced without taking the reactor offline [72]. 2.4.2. Fischer-Tropsch Catalyst Iron (Fe), Cobalt (Co), Nickel (Ni) and Ruthenium (Ru) -based catalysts are active enough to be used in FTS. However, iron and cobalt are the only catalysts utilized in Fischer- Tropsch synthesis [72] due to the various drawbacks of nickel and ruthenium. Nickel is a strong hydrogenating catalyst which forms much more methane then iron or cobalt. Nickel also converts to carbonyls, thus requiring more catalyst to be added. Ruthenium is the most active but is rare and expensive [71]. Table 5 gives the cost comparison of the four catalysts. Table 5: Cost scale of Fischer-Tropsch catalyst in 2001 [73]. Catalyst Cost scale Iron (Fe) 1 Cobalt (Co) 1000 Nickel (Ni) 250 Ruthenium (Ru) 50000 When comparing iron catalysts to cobalt catalysts, iron requires a lower H2/Co ratio from .8 to 1.7 because in the reactor, it performs a water gas shift to increase the required H2/Co ratio [75]. Cobalt requires a water gas shift to be preformed on the syngas before it enters the reactor, to reach its H2/Co ratio of ~2. Cobalt, however has a longer life and is more active [73]. The higher activity of cobalt is visible by looking at an example given by Dry al. et, in which the percent conversion is compared to the bed length for iron and cobalt catalyst. Dry uses the established kinetic equation for cobalt catalysts (2.4.1) [76] and for iron catalysts (2.4.2) [77] to generate Figure 8. 32
kpH 2 pCO Cobalt rate = 2 (2.4.1) ( 1+ bpCO) mpH 2 pCO Iron (Fe) rate = (2.4.2) ( pCO + apH 2O) The k and m constants were chosen so that the percent conversion of both catalysts would be equivalent at the catalyst bed entry at 3.15Mpa, thereby giving them the same intrinsic activity. Figure 8 is the plot comparing the activity of the cobalt catalyst to that of the iron catalyst, in terms of percent conversion at a given bed length. The conversion of the iron catalyst is unchanged when the pressure is increased from 3.15Mpa to 6.3Mpa. The cobalt catalyst displays a better conversion even when the intrinsic activity of iron is increased by a multiple of five [73]. Figure 8: The calculated conversion profiles for LTFT operation with cobalt- and iron- based catalysts. Catalysts are susceptible to poisons from contaminates. To avoid poisoning, contaminates such as tar, hydrogen sulfide, carbonyl sulfide, ammonia, hydrogen cyanide, alkali and dust particles must be removed from the syngas in a gas cleaning process[78]. The higher cost of cobalt makes it critical to prevent poisoning. Table 6 compiled by Hamlinck et al., lists specification for Fischer-Tropsch synthesis and the effectiveness of wet and dry gas cleaning methods [79]. 33
Page 1 and 2: Novel Design of an Integrated Pulp
Page 3 and 4: Table of Contents List of Figures .
Page 5 and 6: List of Figures Figure 1: Price of
Page 7 and 8: 1 Introduction The global transport
Page 9 and 10: 2 Background 2.1 Pulp Mill Backgrou
Page 11 and 12: 2.1.2.2 Chemical Pulping The most c
Page 13 and 14: sodium sulfide and sodium carbonate
Page 15 and 16: process described in the section on
Page 17 and 18: 2.2.1 Low-Temperature Black Liquor
Page 19 and 20: Figure 2: Chemrec gasification proc
Page 21 and 22: Table 3: Average syngas composition
Page 23 and 24: DME than that could be obtained fro
Page 25 and 26: U.S. Patent[58] and European Patent
Page 27 and 28: Figure 4: Topsøe gas phase technol
Page 29 and 30: DME Workshop, Japan (Sept. 7, 2000)
Page 31: 2.4.1. Fischer-Tropsch Reactors The
Page 35 and 36: invention of Fischer-Tropsch in the
Page 37 and 38: Table 7: hydrocarbons and associate
Page 39 and 40: 3 Process Design 3.1 Pulp Mill 3.1.
Page 41 and 42: carbonate is fired in a lime kiln t
Page 43 and 44: lost and the pulp that provides tha
Page 45 and 46: Table 16: General operating paramet
Page 47 and 48: Table 19: Ash analysis of Pittsburg
Page 49 and 50: Table 22: Experimental syngas compo
Page 51 and 52: 3.2.5 Process Options and Flexibili
Page 53 and 54: Nitrogen compounds Nitrogen from th
Page 55 and 56: 3.3.2.3 Reactors A single-step gas
Page 57 and 58: Table 27: FT-diesel fuel synthesis
Page 59 and 60: 3.5.2 Power Generation Process Desi
Page 61 and 62: Figure 21: Schematic of biorefinery
Page 63 and 64: ar) reacts with the fuel in the com
Page 65 and 66: Figure 25showed the detailed energy
Page 67 and 68: 4. Design Summary The DME design an
Page 69 and 70: Figure 27: Mass and energy flow of
Page 71 and 72: References 1. Åhman, M., G. Modig,
Page 73 and 74: 42. R.A. Peascoe, J.R.K., C.R. Hubb
Page 75 and 76: PerformanceSimulation. 2006, Prince
Page 77 and 78: Appendix Appendix A MP Steam Demand
Page 79 and 80: Appendix B: Composite Fuel Blend to
Page 81 and 82: DME Density = 0.67 kg/L (at 20 °C)
Page 83 and 84:
Air Separation Unit Requirements Ba
Page 85 and 86:
Purge gas: CO conversion is 60%, 40
Page 87 and 88:
Appendix D: FTD Synthesis Two diffe
Page 89 and 90:
Table D.3: The hydrocarbon product
Page 91 and 92:
Figure D.3 Mass and energy balance
Page 93 and 94:
Table D.3 Mass and energy balance o
Page 95 and 96:
Appendix E: Heat and Power Generati
Page 97 and 98:
Energy H2O absorbed MW 46.71 Using
Page 99 and 100:
Combustion 2CO+O2→ 2CO2 + 566 kJ/
Page 101 and 102:
Specific Heat (cp) b kJ/kgK 1.072 E
Page 103 and 104:
Specific Heat of Steam (cp) kJ/kgK
Page 105:
Appendix F: Concept Map 105
show all

Novel Design of an Integrated Pulp Mill Biorefinery for the ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?